56K modem technology is designed to work in the case where one end (the server) has a digital path directly from the computing device, through digital elements in the telephone network, to the central office nearest the end user. At that point, the digital signal is converted to analog form and placed on the local analog telephone loop The other end (client) is connected to the other end of the local loop with an analog connection. In this instance, the server can send data at a 56,000 bits/second rate because it can apply digital patterns (corresponding to different analog voltages) synchronized to the rate that those patterns are applied to the analog line by the digital-to-analog converter (codec). Depending on the scheme considered, the path from the client to modem may use a similar scheme, or may use a conventional modulation like ITU-T V.34.
The problem occurs when two such server modems attempt to connect to one another. Because they are both digitally coupled to the public switched telephone network ("PSTN"), they should be able to connect at 64,000 bits/second in both directions (or possibly 56,000 bits/second if an archaic telephone system called robbed-bit signalling is in use).
However, this is not accomplished. Instead, the modems first negotiate the highest speed modulation scheme they both support, using a protocol called V.8 (or V.8bis). Since the 56K protocol is asymmetric, both servers will not see a client, so they will drop to V.34 (33,600 bits/second), which is about half the speed that could otherwise be supported.
Therefore, there is a need in the art for an ability for two 56K modems to communicate with each other over the public switched telephone network at 56,000 bits/second, or even 64,000 bits/second.